Carbon Restoration

Certain processes, such as investment casting, create a decarburized layer on the surface of the part. Microstructurally decarburization is exhibited by ferrite from the surface of the part to some depth, depending on casting variables or prior thermal processes. Often the layer of ferrite is objectionable, due its low strength and wear properties. This condition can be remedied by the process of carbon restoration. This process is essentially carburizing the part such that the surface carbon potential matches the base carbon content of the specified material.

Capabilities

The process of carbon restoration requires an atmosphere furnace using endo-thermic gas as the medium to add carbon to the surface of the components or castings. It is essentially a carburizing heat treatment and thus it is critical that the furnace have a system that controls the carbon content of the furnace. ThermTech has many options for processing parts needing carbon restoration. The sizes of ThermTech’s furnaces capable of carbon restoration range up to 36” x 72” x 48” and an 8000 lbs. maximum loading capacity. All of ThermTech’s furnaces are certified to AMS 2750 for pyrometry.

Process

The critical variables for carbon restoration are the base carbon and chemistry of the material and the depth of decarburization. Once these variables are known a process can be derived for the proper time, temperature and carbon potential to yield a part free from partial or total decarburization. Final hardness and mechanical properties are another consideration. Hardening and carbon restoration can often be achieved in the same cycle depending on alloy. If the parts require machining an annealed microstructure may be required. It is best to discuss the requirements for final properties with the heat treater prior to the submission of the purchase order so that the proper process or processes can be agreed upon.

Recommendations

The general process of carbon restoration applies to a large range of materials. That said the process parameters can vary greatly for each alloy and the final properties that are required for a given component. The most important aspects of carbon restoration are the correct carbon potential to diffuse carbon into the surface of the part and the proper time at heat to assure that the carbon content is uniform from the surface into the part and that the formerly low carbon zone has been totally restored.

Normalizing is one of the simplest heat-treatments that can address refining (or normalizing) the microstructure and equalizing the effects of the range of temperatures the material has been subjected to during the forging operations.

ThermTech is a pioneer in the abilities to polymer quench large section sizes of forgings that require superior mid-radius hardness and mechanical properties for forgings needed by the fracking companies components.

We have come across several customers who perfer their forgings be marquenched in molten salt to minimize the risk of cracking during the quench operations and to minimize distortion on long, thin products.

The full annealing process involves taking a casting to a temperature above the critical eutectoid temperature in the 1475F-1650F range for a length of time commiserate with the cross section size and then slow cooled to promote a ferritic microstructure.

To insure that the steel castings are capable of achieving full surface hardness during subsequent hardening processing the castings may require a carbon restoration of their surfaces and we have several furnaces capable of doing this.

This process involves heating the parts above the critical temperature and slow cooling them in order to create a microstructure both more refined due to recrystallization and softer and more ductile regarding hardness and mechanical properties.

Many machined components have intricate details or section size changes that lend themselves to being crack-prone.We watch for problem jobs like this and we can run them through our neutral hardening salt furnace with molten salt quench to avoid cracking.

Carbonitriding can be performed on both heavy gage stampings and low alloy machined components. Typically the case depths needed are in the 0.003" to 0.020" range due to the low hardenability of the steels involved.

Several people in our Quality Department maintain the specification library, write part number specific processes and manage the sub-contracted mechanical testing to insure your parts are exceeding the mechanical requirements for your application.

A vacuum stress relief of molds allows a more uniform looking textured surface during subsequent usage. We can handle a die or mold up to 36" wide x 32" high x 72" long with a total piece weight of 10,000 pounds.

Some Tool and Die materials like S-5, 52100, O-1, & O-6 require oil quench hardening. ThermTech has several furnaces capable of hardening these materials with the largest being 36" wide x 42" high x 72" long.

Often several tool steels supplied in the as-cast conditions definitely need a carbon restoration due to the high carbon content of those materials and the natural de-carburization environments of the casting processes.

To straighten out a material post-hardening when they are at their most brittle we employ a process involved fixturing the part during the tempering operation where the material has more ductility and takes a set to a straighter/flatter configuration.

Tool & Die products shaped in cylindrical form require straightening by mechanically pressing the parts with some localized heat put on an area to prevent gross cracking due to the brittleness of the material involved.

Gears made from plain carbon steels like 1017, 1018, and 1020 materials and low alloys such as 1117 & 12L14 require ammonia additions at the end of the carburizing process to increase the surface hardness of splines and teeth.

ThermTech has the unique capability of Carburizing gears and quenching them into molten salt to help minimize distortion. We have two furnaces capable of marquenching gears in furnaces with load sizes of 36" wide x 48" high x 72" long.

ThermTech can age harden several varieties of Aluminum to the T-6 or T6 condition. We've aged smaller diameter tubes up to 12' lengths and can handle many varieties of parts up to 60" in diameter to 80" tall.

Stress Relieving can help minimize the distortion seen by the part due to the machining stresses that can be built up by the manufacturing of the part. Contact us for a quote. We can handle a wide variety of sizes for this process.

Many times the end usage of Investment Castings don't require any hardening of the material for the parts to work, however, the parts may require a stress relieve to remove any stress caused by the casting process so the parts maintain their tolerances.

Due to partial or total surface decarburization that stems from the investment casting process a procedure known as carbon restoration is used to restore the proper carbon content at the surface of the parts in question.

Several types of low alloy investment castings require water quench hardening in order to achieve the proper hardness or mechanical properties. These alloys usually are plain carbon steels such as 1018, 1020, 1030, 1035, 1040, & 1045 materials.

Due to most of the investment castings we process being on the small size (less than 5 lbs each) we offer both hand-blast and a rubber belt tumble-blast options to properly and quickly turn around any cleaning requirements.